Co2 capture from dilute sources

ABSTRACT

Systems and methods are provided for separation of CO 2  from dilute source streams. The systems and methods for the separation can include use of contactors that correspond radial flow adsorbent modules that can allow for efficient contact of CO 2 -containing gas with adsorbent beds while also facilitating use of heat transfer fluids in the vicinity of the adsorbent beds to reduce or minimize temperature variations. In particular, the radial flow adsorbent beds can be alternated with regions of axial flow heat transfer conduits to provide thermal management. The radial flow structure for the adsorbent beds combined with axial flow conduits for heat transfer fluids can allow for sufficient temperature control to either a) reduce or minimize temperature variations within the adsorbent beds or b) facilitate performing the separation using temperature as a swing variable for controlling the working capacity of the adsorbent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/787,512 filed Jan. 2, 2019, which is herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

Systems and methods are provided for capture of CO₂ from air or otherdilute CO₂ sources.

BACKGROUND OF THE INVENTION

Capture of CO₂ for sequestration and/or for commercial use is an ongoingarea of interest. In addition to capture of CO₂ at point sources, suchas power plants, direct capture of CO₂ from air can also potentially bevaluable. However, direct air capture of CO₂ can pose a variety ofchallenges.

One general difficulty in performing CO₂ capture is identifying suitableadsorbents and/or adsorbent structures for capture of the CO₂. Thisgeneral difficulty is exacerbated when attempting to perform CO₂ capturefrom relatively dilute sources. Conventionally, layered bed structures(sometimes referred to as Napoleons) have been used when attempting toperform capture of CO₂ from low concentration sources. The goal of suchlayered bed structures can be to provide a high adsorbent capacity perunit volume, a high adsorbent utilization, or a combination thereof.

U.S. Pat. No. 8,268,043 describes a layered adsorbent bed contactor foruse in a gas separator plant. The adsorbent bed design is described asproviding low inlet void volumes, large bed frontal areas, and short beddepths. To achieve this, the adsorbent beds correspond to thin slabs,with gas being passed through the beds along the thin dimension. Theresulting design is described as providing high adsorbent utilization.

U.S. Patent Application Publication 2017/0326494 describes a layeredadsorbent structure corresponding to a plurality of layers of adsorbentparticles that are held in place using semi-permeable fabric material.The adsorbent structure is described as being suitable for performingdirect air capture of CO₂. The layers are arranged in a parallel mannerwith a defined narrow spacing between layers.

U.S. Pat. No. 10,029,205 describes a separation process performed usinga two stage radially disposed adsorbent structure. The first adsorbentstage can include a metal organic framework adsorbent, while the secondstage can include an adsorbent that is suitable for desorption of CO₂ bydisplacement with steam. The two stage adsorbent structure is describedas being suitable for separation of CO₂ from streams having as low as 3vol % CO₂.

SUMMARY OF THE INVENTION

In one aspect, a method for performing a separation on a diluteCO₂-containing feed is provided. The method can include passing a feedcomprising a CO₂ content of 5000 vppm or less and a first H₂O contentinto a radial flow adsorbent bed module comprising alternating adsorbentbed sections and heat transfer sections to form adsorbed CO₂ and aCO₂-depleted stream. The adsorbent beds can include a bed inner surfacethat faces a central axis of the radial flow adsorbent bed module and abed outer surface at a larger radial distance from the central axis thanthe bed inner surface. The heat transfer sections can include a transfersection inner surface that faces a central axis of the radial flowadsorbent bed module and a transfer section outer surface at a largerradial distance from the central axis than the interior surface. The bedinner surfaces and the transfer section inner surfaces can define acentral volume. The adsorbent beds can include one or more adsorbentshaving amine functional groups. The feed can be passed through theadsorbent beds under adsorption conditions at a first temperature andsubstantially along a radial direction of the radial flow adsorbent bedmodule. The method can further include desorbing at least a portion ofthe adsorbed CO₂ in the presence of a purge gas under desorptionconditions to form a CO₂-enriched purge gas comprising a CO₂ contentgreater than the CO₂ content of the feed, the desorption conditionscomprising at least one of a desorption temperature higher than thefirst temperature and an H₂O content in the purge gas that is greaterthan the first H₂O content. The purge gas can be passed through theadsorbent beds substantially along the radial direction of the radialflow adsorbent bed module. The method can further include passing,during the adsorbing and the desorbing, one or more heat transfer fluidsthrough the heat transfer sections substantially along an axialdirection of the radial flow adsorbent bed module.

In another aspect, a system for separating CO₂ from a dilute feed isprovided. The system can include a plurality of radial flow adsorbentbed modules arranged in a Napoleon configuration. A radial flowadsorbent bed module in the Napoleon configuration can include aplurality of adsorbent bed sections, the adsorbent bed sectionsincluding a bed inner surface that faces a central axis of the radialflow adsorbent bed module and a bed outer surface at a larger radialdistance from the central axis than the bed inner surface. The adsorbentbeds can include one or more adsorbents having amine functional groups.A radial flow adsorbent bed module can further include a plurality ofheat transfer sections, the plurality of heat transfer sectionsalternating with the plurality of adsorbent bed sections in the radialflow adsorbent bed module. The heat transfer sections can include one ormore heat transfer fluid conduits oriented substantially along an axialdirection of the radial flow adsorbent bed module. The heat transfersections can include a transfer section inner surface that faces acentral axis of the radial flow adsorbent bed module and a transfersection outer surface at a larger radial distance from the central axisthan the interior surface. The bed inner surfaces and the transfersection inner surfaces can define a central volume, so that the radialflow adsorbent bed module corresponds to a substantially annular shape.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an example of a radial flow adsorbent module.

FIG. 2 shows a top view of a radial flow adsorbent module

FIG. 3 shows an example of a configuration including a plurality ofradial flow adsorbent modules.

FIG. 4 shows an example of a configuration corresponding to a Napoleonconfiguration of radial flow adsorbent modules.

FIG. 5 shows a top view of an annular Napoleon configuration of radialflow adsorbent modules.

FIG. 6 shows an example of a flow pattern in an annular Napoleonconfiguration of radial flow adsorbent modules.

FIG. 7 shows an example of counter-current flow patterns for adsorptionand desorption in an annular Napoleon configuration of radial flowadsorbent modules.

FIG. 8 shows another example of a flow pattern in an annular Napoleonconfiguration of radial flow adsorbent modules.

FIG. 9 shows an example of separating CO₂ from a dilute feed to providean enriched CO₂ stream for use in a bio-reactor.

FIG. 10 shows another example of a flow pattern in an annular Napoleonconfiguration of radial flow adsorbent modules.

DETAILED DESCRIPTION OF THE EMBODIMENTS

All numerical values within the detailed description and the claimsherein are modified by “about” or “approximately” the indicated value,and take into account experimental error and variations that would beexpected by a person having ordinary skill in the art.

Overview

In various aspects, systems and methods are provided for separation ofCO₂ from dilute source streams, such as source streams having a CO₂content of 5000 vppm or less, or 3000 vppm or less, or 1000 vppm orless, or 500 vppm or less, such as down to 100 vppm of possibly stilllower. The systems and methods for the separation can include use ofcontactors that correspond to one or more radial flow adsorbent modulesthat can allow for efficient contact of CO₂-containing gas withadsorbent beds while also facilitating use of heat transfer fluids inthe vicinity of the adsorbent beds to reduce or minimize temperaturevariations. In particular, the radial flow adsorbent beds can bealternated with regions of axial flow heat transfer conduits to providethermal management. The radial flow structure for the adsorbent bedscombined with axial flow conduits for heat transfer fluids can allow forsufficient temperature control to either a) reduce or minimizetemperature variations within the adsorbent beds or b) facilitateperforming the separation using temperature as a swing variable forcontrolling the working capacity of the adsorbent.

Conventionally, thin layer adsorbent beds have been used when attemptingto separate a dilute component from a feed. Thin layer adsorbent bedsare traditionally believed to provide several advantages for performingdilute separations. Such traditional advantages include providing alarge exposure area for the adsorbent relative to the adsorbent volume,and the ability to stack the layered beds to provide a high density ofadsorbent relative to the volume of the contactor. However, maintainingdesired control over temperature can pose problems. In particular, thedistributed nature of the thin layer adsorbent beds can make itdifficult to bring heat exchange fluids in close proximity to theadsorbent without also blocking large portions of the surface area fromcontact with the feed. U.S. Patent Application Publication 2017/0326494describes use of metal sheets as secondary heat transfer surfaces in aneffort to overcome this difficulty.

It has been discovered that a radial flow configuration for adsorbentbeds can provide a variety of advantages when attempting to separate adilute species (such as CO₂) from a feedstream. In particular, a radialflow contactor can be used where the adsorbent beds correspond to aseries of adsorbent beds arranged around a central volume that containsa central axis of the annular structure. The adsorbent beds can beseparated by heat transfer sections that include, for example, axialflow conduits for passing heat transfer fluids in proximity to theadsorbent beds. In some aspects, the axial flow conduits can correspondto conduits that are substantially aligned with the axial directionwhile in proximity to the adsorbent beds. In other aspects, the axialflow conduits can include one or more turns, so long as the netdirection of flow of gas through the adsorbent beds can be roughlyperpendicular to the net direction of flow of heat transfer fluidthrough the heat transfer sections. For example, the flow of gas throughthe adsorbent beds can be in a radial direction while the flow of heattransfer fluid through the heat transfer section can be in an axialdirection. This type of configuration can allow for efficient heattransfer from the adsorbent beds and heat transfer fluid conduits whilestill providing a compact footprint for the adsorbent bed modules. Themodules can also be readily scaled into larger assemblies. Optionally,the series of adsorbent beds can correspond to wedges, so that the widthof the beds varies with distance from the central axis.

The use of alternating heat transfer sections in the radial flowadsorbent modules can allow heat transfer conduits to be placed in closeproximity to the adsorbent beds in an efficient manner. This can allowfor improved temperature control in comparison with a stacked bedstructure. This can facilitate, for example, a separation to beperformed using concentration gradients as the swing variable (i.e.,displacement adsorption and/or displacement desorption) while havingreduced or minimized temperature differences between the adsorption anddesorption steps. This can provide improved working capacity for anadsorbent when using displacement desorption for a separation. In someaspects, both temperature and concentration gradients can be used asswing variables.

The ability to provide improved heat management and/or temperaturecontrol can be beneficial for improving the working capacity of theadsorbent. The nature of the heat management and/or temperature controlcan vary depending on the type of separation being performed. Forexample, during a separation based on displacement desorption, in someinstances it can be beneficial to maintain the temperature of theadsorbent at a relatively constant value. Due to the dilute nature ofthe CO₂ in the feed for separation, the difference in CO₂ loadingbetween the maximum during the adsorption step and the minimum duringthe desorption can be relatively modest. Thus, small changes in thetemperature during adsorption and/or desorption can have a substantialimpact on loading. By using a combination of radial flow adsorbent bedswith adjacent axial flow heat transfer sections, temperature control canbe improved. In aspects involving displacement desorption, the improvedtemperature control can optionally allow for temperature differencesbetween the average bed temperature at the end of an adsorption step andthe average bed temperature at the end of a desorption step of 5° C. orless, or 3° C. or less. In some aspects, providing improved thermalcontrol can correspond to having a difference in average bed temperaturein an adsorbent bed between the beginning of an adsorption step and theend of the adsorption step of 5° C. or less, or 3° C. or less. In someaspects, providing improved thermal control can correspond to having adifference in average bed temperature in an adsorbent bed between thebeginning of a desorption step and the end of the desorption step of 5°C. or less, or 3° C. or less. The temperature in an adsorbent bed can bemeasured by any convenient method, such as by use of one or morethermocouples. The average bed temperature can be determined bymeasuring a) the temperature of the bed at the outer surface of theradial bed and b) at the inner surface of the radial bed (i.e., thesurface facing the inside the annular volume of the radial module).

As another example, in aspects where the separation is based in part ontemperature swing adsorption, providing improved thermal control cancorrespond to having a difference in average bed temperature in anadsorbent bed between the beginning of an adsorption step and the end ofthe adsorption step of 10° C. or less, or 5° C. or less. Additionally oralternately, providing improved thermal control can correspond to havinga difference in average bed temperature in an adsorbent bed between thebeginning of a desorption step and the end of the desorption step of 10°C. or less, or 5° C. or less. It is noted that temperature swingadsorption can in some situations involve a difference in temperaturebetween the adsorption step and the desorption step of 50° C. to 100° C.

In some aspects, the ability to provide improved heat management canalso be beneficial from a practical standpoint for performing CO₂separation on a dilute feed using commercially relevant volumes. Whenseparating CO₂ from a dilute feed, the energy consumed per mole ofseparated CO₂ can be relatively high compared to separation from aconventional (higher concentration) feed. Using a radial flow adsorbentmodule as described herein, a first portion of the adsorbent beds can beoperated in adsorption mode, which can generate a heated gas stream dueto the exotherm during adsorption. A portion of the heated gas streamfrom the bed operating under adsorption conditions can be used as thegas stream for a bed operating under desorption conditions. This canallow the heat generated during adsorption to be at least partiallyrecovered in a corresponding desorption step, allowing for overall lowerenergy consumption.

Radial Flow Adsorbent Bed Modules

In various aspects, radial flow adsorbent bed modules can be used tofacilitate separation of CO₂ from dilute feeds. The radial flow modulescan be composed of annular modules of alternating adsorbent bed sectionsand heat transfer sections. If desired, a plurality of modules can thenbe arranged in an assembly, array, or other convenient grouping ofmultiple modules to facilitate larger scale separation. An example of agrouping of multiple modules can be a Napoleon, such as a Napoleon basedon stacking of the radial flow adsorbent bed modules in rows and/orcolumns, or a Napoleon based on organizing the radial flow adsorbent bedmodules into a series of stacked annular shapes around a common centralannular volume (referred to herein as an annular Napoleon).

FIG. 1 and FIG. 2 show a perspective view and a top view of an exampleof an annular module 100, respectively. In FIG. 1, the annular moduleincludes alternating adsorbent bed sections 110 and heat transfersections 120. The flow path through the adsorbent bed sections 110corresponds to a radial flow path. One entry or exit location for gas isthrough outer surface 112 of an adsorbent bed section 110. The otherentry or exit location is inner surface 114, which is adjacent tointerior or central volume 130 of the annular shape. Central axis 135 iswithin the interior or central volume 130. In FIG. 2, outer surface 112and inner surface 114 correspond to arcuate surfaces that havecurvatures that substantially correspond to the curvature of the annularshape. In other aspects, outer edge 112 and/or inner edge 114 can havesurfaces that differ from the curvature of the annular shape, such asflat surfaces. In FIG. 1 and FIG. 2, the adsorbent bed sections 110 areshown as having a wedge shape, where the width of the section increaseswith increasing distance from central axis 135. In other aspects, theadsorbent bed sections 110 can have any other convenient shape that isconsistent with forming a roughly or approximately annular shape for themodule 100, such as a rectangular cuboid shape or other parallelepipedshape.

The annular module 100 also includes heat transfer sections 120. Heattransfer sections 120 can include one or more conduits containing a heattransfer fluid, such as steam. In some aspects, the flow path for theheat transfer fluid conduits can be in a direction 125 that issubstantially parallel to the central axis 135. In some aspects, the netflow direction of the heat transfer fluid can be substantially in anaxial direction, but the flow path can include changes in flow directionwhile within the heat transfer section(s) 120. The heat transfersections 120 can each include any convenient number of heat transferfluid conduits. The heat transfer sections can optionally but preferablybe impermeable to gas flow, so that any flow of gases between theexterior of annular module 100 and the central volume 130 is forced topass either through an adsorbent bed section 110 or through an exit atthe bottom or top of central volume 130.

Any convenient number of alternating adsorbent bed sections 110 and heattransfer sections 120 can be used to form an annular module 100. Theexample of an annular module 100 shown in FIG. 1 and FIG. 2 includes sixadsorbent bed sections 110 and six heat transfer sections 120. Thenumber of adsorbent bed sections 110 can be selected, for example, sothat a sufficient number of heat transfer sections 120 are present toprovide a desired level of temperature control. The inner radius andouter radius of annular module 100 can be selected based on anyconvenient consideration. For example, the inner radius and outer radiuscan be selected to provide a desired pressure drop, to provide a desiredamount of adsorbent capacity, or a combination thereof. Examples oftypical values for the inner radius can be 0.5 m-1.0 m; for thethickness of the adsorbent bed can be 1.0 m-2.0 m; and for the outerradius can be 1.5 m to 3.0 m. Examples of typical values for the lengthof the annular module can range from 5.0 m-15 m.

With reference to FIG. 1, it is to be understood that the flow path ofthe various feed and product streams disclosed herein, and theassociated headers, valve manipulations, etc. would be readilyrecognizable to one of ordinary skill in the art. Accordingly, suchmechanisms may not be shown in the figures.

For performing larger scale separations, a plurality of radial flowmodules such as the module shown in FIG. 1 can be arranged to allow theplurality of modules to separate CO₂ from a common gas flow. FIG. 3shows an example of arranging a plurality of radial flow modules 220within a common volume 210 having a shape that roughly corresponds to acylinder. It is noted that the common volume 210 is optional, as theremay be no enclosure for the modules or the shape and/or size of theenclosure may not be related to the arrangement of the radial flowmodules 220. In the configuration shown in FIG. 3, one example ofoperation could be to pass a dilute CO₂ flow into the common volume 210during the adsorption step. The dilute CO₂ flow could pass radiallythrough the adsorbent beds into the central volumes 228 of individualmodules 220. The CO₂-depleted flow can then pass out of central volumes228 into a manifold (not shown) or other piping. At the end of theadsorption step, the flow can then be changed in a desired manner. Forexample, for a separation based on temperature swing adsorption, thetemperature in the radial flow modules 220 can be increased byincreasing the temperature of the heat transfer liquid being passedthrough each module. A purge gas (optionally heated) can also beintroduced, so that the purge gas becomes a CO₂-enriched stream as CO₂is desorbed from the adsorbent beds. In some aspects, the purge gas cancorrespond to a co-current purge, so that the purge gas is passed intocommon volume 210, then through the adsorbent beds of radial flowmodules 220, and then into central volumes 228 to exit from theplurality of modules. Alternatively, a counter-current purge could beused, so that the purge gas enters the plurality of radial flow modulesvia central volumes 228, and then is passed through the adsorbent bedsof radial flow modules 220 to enter the common volume. At the end of thedesorption step, the temperature of the radial flow modules can bereduced in part by reducing the temperature of the heat transfer fluidthat is passed through the radial flow modules 220. It is noted thatdisplacement desorption can follow a similar cycle, with steam beingused as the purge gas. With regard to temperature control, the heattransfer fluids can be used to reduce or minimize temperature swings inthe radial flow modules during adsorption and desorption, if desired.

Another option for arranging a plurality of modules can be to constructa “Napoleon” structure, as shown in FIG. 4. In the configuration shownin FIG. 4, instead of using thin layer adsorbent beds to form theNapoleon structure, the Napoleon is formed from layers of the radialflow modules 320. The (optional) common volume 310 has a different shapecompared with FIG. 3, but otherwise the operation of the Napoleonarrangement in FIG. 4 can be similar to the operation in FIG. 3.

Yet another option can be to take advantage of the geometry of theradial flow modules to form a different type of Napoleon structure. FIG.5 shows a top view of an example of arranging a plurality of the radialflow modules 420 to form an annular shape 450. In the example shown inFIG. 5, the shaded areas correspond to the radial flow module 420, withopen intervals 435 between the radial flow modules 420 to allowentry/exit of gas through the adsorbent beds of the radial flow modules420. The top view in FIG. 5 shows only one annular layer of a potentialNapoleon structure. As shown in FIG. 6, any convenient number of annularlayers 460 can be stacked, to create a Napoleon structure with a commoncentral annular volume 470 in the center. It is noted that this type ofannular Napoleon structure can simplify the piping or manifold requiredfor managing the gas flows. In particular, the central axes of theradial flow modules 420 each exit into the common central annular volume470 of the Napoleon structure. This can allow input flows to be readilydistributed and/or output flows to be ready aggregated into a commonpipe.

The ability to create an annular Napoleon configuration using the radialflow modules can provide additional options for managing the flowsduring an adsorption/desorption cycle. For example, FIG. 7 shows anexample of two potential flow schemes for an annular Napoleonconfiguration. The flow schemes in FIG. 7 can be used individually, orthe flow schemes can be paired to create a counter-current flow schemefor the adsorption and desorption steps of a separation cycle. In orderto simplify the description, the flow schemes in FIG. 7 are describedfor use as counter-current flows, with the left hand portion of FIG. 7corresponding to adsorption and the right hand portion corresponding todesorption.

In FIG. 7, the left-hand portion can correspond to flows for use duringthe adsorption phase of a separation cycle. In the left-hand portion ofFIG. 7, the dilute CO₂-containing feed 701 can be introduced into thespace 722 between the radial flow modules 720 in (optional) commonvolume 710. This can correspond to introducing the feed into a commonvolume that encloses the Napoleon structure, or any other convenientmethod of introducing the dilute CO₂-containing feed to space around theradial flow modules can be used. The feed can be provided withsufficient pressure to allow the feed to pass through the adsorbent bedsof the radial flow modules 720 to enter the central volumes of theradial flow modules. As the feed passes through the adsorbent beds, CO₂is adsorbed. The resulting CO₂-depleted feed can then exit the centralvolumes of the radial flow modules 720 to pass into the common centralannular volume 750 of the Napoleon structure. The gas flow into thecommon central annular volume 750 can then be carried away to anyconvenient process and/or purged into the atmosphere.

At the end of the adsorption cycle, the flows can be changed to create aCO₂-enriched purge stream 799 by desorption of CO₂ from the adsorbentbeds. The right-hand portion of FIG. 7 shows a counter current flowscheme for creating the CO₂-enriched purge stream. In the right-handportion of FIG. 7, the purge gas 791 can be introduced into the commoncentral annular volume of the Napoleon structure. The purge gas can thenenter the radial flow modules via the central axis of each module. CO₂desorbed from the adsorbent can be incorporated into the purge gas,which then exits into the common volume surrounding the Napoleon.

FIG. 10 shows another example of a flow scheme for operating a Napoleonconfiguration of the radial flow adsorbent modules. FIG. 10 uses aNapoleon configuration of radial flow adsorbent modules that is in someways similar to FIG. 7, but with different connectivity between themodules and external pipes and valving. In FIG. 10, an input flow 1001can be introduced into common volume 1010 during an adsorption step. Inthe aspect shown in FIG. 10, the flow paths in common volume 1010 can beconfigured so that input flow 1001 is substantially directed into thecentral volumes 1028 of radial flow modules 1020. During adsorption,valve 1052 can be closed, so that feed introduced into central volumes1028 will exit radially from the radial flow modules 1020. It is notedcentral volume 1050 can receive an initial portion of the flow untilsufficient pressure builds up in central volume 1050 to causesubstantially all of the flow to exit radially from radial flow modules1020. After exiting radially from the radial flow modules 1020, the flowcan pass out of the common volume 1010 as exit flow 1029.

During a desorption step, valve 1052 can be opened, so that a purge flow1081 can pass into central volume 1050. One or more valves 1062 can beclosed, so that the purge flow 1081 cannot leave the central volume 1050along the same path as exit₂₂ flow 1029. Instead, purge flow 1081 canpass into the central volumes 1022 of the radial flow modules 1020, andthe purge gas (including desorbed CO₂) can exit as CO₂-enriched stream1089.

FIG. 8 shows yet another example of a flow scheme for operating aNapoleon configuration of the radial flow adsorbent modules. In theconfiguration shown in FIG. 8, a first group of modules 820 are operatedin an adsorption mode. A dilute CO₂-containing feed 801 can beintroduced into the space 822 around the modules 820. CO₂ can beadsorbed by the adsorbent in modules 820. This results in formation of aCO₂-depleted feed. Due to the heat generated during adsorption, theCO₂-depleted feed can also be at a higher temperature. A portion of thishigher temperature, CO₂-depleted feed can be passed out of the contactorvia the common central annular volume 850. A remaining portion of thehigher temperature, CO₂-depleted feed can be used as a purge gas fordesorption of CO₂ from a second group of modules 870. By using a smallervolume of gas relative to the amount of feed 801, a CO₂-enriched product885 can be produced as the remaining portion of the purge gas passesthrough second group of modules 870.

Simulated Moving Bed Configurations

The flow schemes shown in FIG. 7, FIG. 8 and FIG. 10 are examples offlow schemes that can be implemented as a simulated moving bed. Whenoperating an adsorbent as a simulated moving bed, the adsorbent can beexposed to a series of different flows, with the entry location for eachflow rotating or moving by one position (or another fixed number ofpositions) after each time interval.

As another example of a potential simulated moving bed implementation,displacement desorption can be used for separation of CO₂ from air. Thiscan reduce or minimize the need to perform temperature swing adsorptionand/or pressure swing adsorption. The adsorbent can correspond to, forexample, a sorbent based on quaternary ammonium sites incorporated intoa polymer and formed into particles for fixed bed use. The input feedcan correspond to air, which typically has a CO₂ concentration ofroughly 400 vppm. The sorbent can be effective for adsorption of roughly60% of the CO₂ from the air. This adsorbed CO₂ can then be desorbedusing a purge stream corresponding to humidified air. This can achieve aCO₂ concentration in the purge stream of roughly 1000 vppm. TheCO₂-enriched purge stream can be used, for example, as a feed forformation of a further CO₂-enrichment process or as a CO₂ source streamfor growth of algae or other biomass.

The relative flows of air during the adsorption and purge steps can bein a ratio of 2.5 volumes of input air to 1.0 volumes of enriched air.Based on this ratio, a convenient configuration can be to have 5adsorption beds for every 2 displacement beds. These beds could bearranged in a Simulated Moving Bed arrangement, with input air dividedequally among 5 beds (or possibly 10 beds) and displacement (humidified)air divided equally among 2 beds (or possibly 4 beds). Valving wouldprogress stepwise to “move” each bed through 5 capture steps followed by2 displacement steps, with a complete cycle requiring 7 steps. Totalinlet flow could be, for example, roughly 100 m³ per second, with theenriched air displacement flow corresponding to roughly 40 m³ persecond. Each bed, whether capture or displacement, could have a flow ofroughly 20 m³ per second. For such a flow, the adsorbent structurewithin a radial flow module can correspond to layered beds of adsorbentbased on pressure drop considerations.

Examples of Adsorbent Structures

In various aspects, the adsorbent bed sections can correspond to anytype of structure, either rigid or non-rigid, that includes orincorporates an adsorbent suitable for adsorption of a gas componentduring a swing adsorption process. This can include conventionalcontactor adsorbent structures, such as parallel plate contactors,adsorbent monoliths, and other conventional structures. This can alsoinclude non-rigid structures, such as flexible, curtain-like, and/orfabric-like adsorbents. Still other adsorbent structures can correspondto beds of adsorbent particles, either in a conventional adsorbent bedconfiguration or in a non-traditional configuration, such as use of bedof adsorbent particles under trickle flow conditions.

An example of a suitable contactor can correspond to a parallel channelcontactor in which the parallel channels are formed from laminatedsheets containing adsorbent material. Laminates, laminates of sheets, orlaminates of corrugated sheets can be used in pressure and/ortemperature swing adsorption processes. Laminates of sheets are known inthe art and are disclosed in U.S. Patent Application PublicationUS2006/0169142 A1 and U.S. Pat. No. 7,094,275. When the adsorbent iscoated onto a geometric structure or components of a geometric structurethat are laminated together, the adsorbent can be applied using anysuitable liquid phase coating techniques. Non-limiting examples ofliquid phase coating techniques that can be used in the practice of thepresent disclosure include slurry coating, dip coating, slip coating,spin coating, hydrothermal film formation and hydrothermal growth. Whenthe geometric structure is formed from a laminate, the laminate can beformed from any material to which the adsorbent of the presentdisclosure can be coated. The coating can be done before or after thematerial is laminated. In all these cases, the adsorbent is coated ontoa material that is used for the geometric shape of the contactor.Non-limiting examples of such materials include glass fibers, milledglass fiber, glass fiber cloth, fiber glass, fiber glass scrim, ceramicfibers, metallic woven wire mesh, expanded metal, embossed metal,surface-treated materials, including surface-treated metals, metal foil,metal mesh, carbon-fiber, cellulosic materials, polymeric materials,hollow fibers, metal foils, heat exchange surfaces, and combinations ofthese materials. Coated supports typically have two major opposingsurfaces, and one or both of these surfaces can be coated with theadsorbent material. When the coated support is comprised of hollowfibers, the coating extends around the circumference of the fiber.Further support sheets may be individual, presized sheets, or they maybe made of a continuous sheet of material. The thickness of thesubstrate, plus applied adsorbent or other materials (such as desiccant,catalyst, etc.), typically ranges from about 10 micrometers to about2000 micrometers, more typically from about 150 micrometers to about 300micrometers. Other examples of suitable structures can include thetriply-periodic minimal surface area contactors, as described in U.S.Pat. No. 9,440,216.

In various aspects, the radial flow adsorbent modules can be beneficialfor separation of CO₂ from a dilute feed stream. The dilute feed streamcan have a CO₂ concentration of 5000 vppm or less, or 1000 vppm or less,or 400 vppm or less, such as 100 vppm to 5000 vppm, or 100 vppm to 1000vppm. The dilute stream can be delivered to the adsorbent structure at atemperature that is generally between 40° C. and 90° C. The pressure ofthe stream can be relatively low, such as 2 bar-a or less.

Various types of adsorbents can potentially be used with a radial flowadsorbent module, such as the radial flow adsorbent module configurationshown in FIG. 1. For example, adsorbents which include amine functionalgroups can be suitable for CO₂ adsorption. In some aspects, theadsorbent can correspond to an amine-appended metal-organic-framework(MOF) adsorbent. MOF adsorbents can be suitable for use in temperatureswing adsorption methods. Based on the step-change nature of the CO₂adsorption on a MOF adsorbent, variations in temperature can be used toswitch between adsorption and desorption. Examples of MOF adsorbents aredescribed in an article by McDonald et al. published in Nature, vol.519, pages 303-308 (2015).

In other aspects, non-MOF adsorbents can be used. Non-MOF adsorbents,which typically exhibit Langmuir-type adsorption curves, can includeamine functionalized or amine double-functionalized adsorbents, suchfunctionalized silica gel adsorbents. Other examples of suitableadsorbents can correspond to ion exchange resin type materials.

Swing Adsorption Processes

Swing adsorption processes can have an adsorption step in which a feedmixture (typically in the gas phase) is flowed over an adsorbent thatcan preferentially adsorb a more readily adsorbed component relative toa less readily adsorbed component. A component may be more readilyadsorbed because of kinetic or equilibrium properties of the adsorbent.The adsorbent is typically contained in a contactor that is part of theswing adsorption unit. In some aspects, a plurality of contactors can beused as part of a swing adsorption system. This can allow adsorption anddesorption to be performed as a continuous process, with one or morecontactors being used for adsorption while one or more additionalcontactors are used for desorption. As contactors approach a desiredand/or maximum loading during adsorption and/or approach a desiredand/or complete desorption under the desorption conditions, the flows tothe contactors can be switched between adsorption and desorption. It isnoted that after the desorption step, the adsorbent may retain asubstantial loading of the gas component.

When separating CO₂ from a dilute feed, the loading of the adsorbentduring the adsorption/desorption cycle can be lower than the loading fora conventional separation. In various aspects, the loading of theadsorbent with the adsorbed gas component at the end of the desorptionstep can be 0.01 mol/kg or more, or 0.05 mol/kg or more, or 0.1 mol/kgor more, or 0.3 mol/kg or more. For example, the loading can be 0.01mol/kg to 1.0 mol/kg, or 0.1 mol/kg to 1.0 mol/kg, or 0.01 mol/kg to 0.5mol/kg. Additionally or alternately, the loading at the end of thedesorption step can be characterized relative to the loading at the endof the prior adsorption step. The adsorbent loading at the end of thedesorption step can be 0.1% or more of the adsorbent loading at the endof the prior adsorption step, or 1% or more, or 5% or more, or 10% ormore, or 20% or more, or 30% or more. Additionally or alternately, theadsorbent loading at the end of the desorption step can be 70% or lessof the loading at the end of the prior desorption step, or 50% or less,or 30% or less, or 10% or less. For example, the adsorbent loading atthe end of the desorption step can be 0.1% to 70% of the loading at theend of the prior adsorption step, or 1.0% to 70%, or 0.1% to 30%, or1.0% to 30%.

The method of adsorbent regeneration designates the type of swingadsorption process. For separation of dilute feeds, temperature swingadsorption (TSA) and displacement desorption (DD) processes can be used.Although pressure swing adsorption (PSA) processes are also generallyknown for separation of gas phase components, due to the lowconcentration of CO₂ in a dilute feed, pressure swing processes may havelower effectiveness.

Temperature Swing Adsorption

Temperature swing adsorption (TSA) processes can employ an adsorbentthat is repeatedly cycled through at least two steps—an adsorption stepand a thermally assisted regeneration step. TSA processes rely on thefact that gases under pressure tend to be adsorbed within the porestructure of the microporous adsorbent materials. When the temperatureof the adsorbent is increased, the adsorbed gas is released, ordesorbed. By cyclically swinging the temperature of adsorbent beds, TSAprocesses can be used to separate gases in a mixture when used with anadsorbent that is selective for one or more of the components in a gasmixture.

Regeneration of the adsorbent can be achieved by heating the adsorbentto an effective temperature to desorb target components from theadsorbent. The adsorbent can then be cooled so that another adsorptionstep can be completed. Such cooling may be supplied by a cooling fluideither directly or indirectly. The temperature swing adsorption processcan be conducted with rapid cycles, in which case they are referred toas rapid cycle temperature swing adsorption (RCTSA). A rapid cyclethermal swing adsorption process is defined as one in which the cycletime between successive adsorption steps is less than about 10 minutes,preferably less than about 2 minutes, for example less than about 1minute. RC-TSA processes can be used to obtain very high productrecoveries in the excess of 90 vol %, for example greater than 95 vol %or, in some cases, greater than 98 vol %. The term “adsorption” as usedherein includes physisorption, chemisorption, and condensation onto asolid support, absorption into a solid supported liquid, chemisorptioninto a solid supported liquid, and combinations thereof.

It is noted that a TSA cycle can also typically include a change in thetemperature of the adsorbent from the temperature for the adsorptionstep to the temperature for the desorption step. The adsorption step canbe defined based on the time when the gas flow is started for the inputgas containing the component for adsorption and when the gas flow isstopped. The desorption step can be defined based on the time when gasbeing desorbed from the adsorbent is collected to the time collection isstopped. Any time in the cycle outside of those steps can be used foradditional adjustment of the adsorbent temperature. A potentialadvantage of a TSA separation can be that the process can be performedat a convenient pressure, or with a small amount of variation around aconvenient pressure. For example, a goal of a TSA separation can be todevelop a substantially pure stream of a gas component that is adsorbedand then desorbed. In this type of aspect, a convenient pressure for thedesorption step can be a temperature of about 1 bar (0.1 MPa) or less.Attempting to desorb a stream at greater than about 0.1 MPa can requiresubstantial additional temperature increase for desorption.Additionally, ambient pressure can be a convenient pressure for theadsorption step as well, as many streams containing a gas component foradsorption can correspond to “waste” or flue gas streams that may be atlow pressure. In some aspects, the pressure difference between theadsorption and desorption steps can be 1 MPa or less, or 0.2 MPa orless, or 0.1 MPa or less, or 0.05 MPa or less, or 0.01 MPa or less.

A variety of types of solid adsorbents are available for separation ofcomponents from a gas flow using temperature swing adsorption (TSA).During a conventional TSA process, at least one component in a gas flowcan be preferentially adsorbed by the solid adsorbent, resulting in astream with a reduced concentration of the adsorbed component. Theadsorbed component can then be desorbed and/or displaced from the solidadsorbent, optionally to form a stream having an increased concentrationof the adsorbed component.

One of the ongoing challenges with swing adsorption processes isbalancing between the desire to increase the working capacity of theadsorbent and the desire to reduce the cycle time. For an idealizedprocess, the working capacity of an adsorbent can be increased byincreasing the severity of the difference between the conditions duringadsorption and desorption of a target component that is adsorbed out ofa gas flow. This can correspond to increasing the difference in pressurebetween adsorption and desorption (typically for PSA), increasing thedifference in temperature between adsorption and desorption (typicallyfor TSA), or a combination thereof.

In practical application, the amount of pressure and/or temperaturedifference between adsorption and desorption can be limited by a desireto improve total cycle time. Increasing the differential in pressureand/or temperature between adsorption and desorption can cause acorresponding increase in the time required for transitioning betweenthe adsorption and desorption portions of a cycle. This can include oneor both of the transition from adsorption to desorption or thetransition from desorption to adsorption.

A further complication in swing adsorption processes can be related toachieving full working capacity and/or achieving full restoration of theadsorbent monolith to a desired state prior to the next adsorption step.Equilibrium adsorption isotherms can describe the potential workingcapacity that may be achieved during a full swing adsorption cycle.However, achieving a desired desorption condition does not guaranteethat equilibrium is reached at that condition. For example, intemperature swing adsorption, it can be desirable to reduce or minimizethe desorption temperature so long as the temperature still achieves adesired amount of desorption. This can often correspond to a temperatureof less than about 200° C. At such temperatures, desorption toequilibrium values may take a long time relative to a cycle time, asrandom fluctuations within the temperature ensemble state may be neededto achieve desorption of individual adsorbed compounds. It is noted thatit may be preferable to operate a swing adsorption cycle withoutreaching the final equilibrium value for the adsorption step and/or thedesorption step. While such operation may reduce the actual workingcapacity of the adsorbent relative to the potential working capacity,ending the adsorption step and/or desorption step prior to reachingequilibrium can substantially reduce the cycle time in some instances.

Displacement Adsorption/Desorption Processes

Displacement Adsorption/Desorption (“DD”) processes employ gas-solidscontactors in which the sorbent is alternately exposed to the feed gasand to steam wherein the gas and steam are essentially at the sametemperature. In the steaming step the carbon dioxide adsorbed from thegas is released from the sorbent by a combination of concentration swingand desorptive displacement, thereby regenerating the sorbent forre-use. No external application or removal of heat is used, and theprocess operates at essentially constant pressure. The process isnotably identifiable and distinguishable and beneficial as compared topressure swing or partial pressure swing separation in that during theadsorption of CO₂ the bed temperature decreases below the average bedtemperature as determined over the entire cycle and during CO₂displacement/desorption the bed temperature increases above the average.The process is further distinguished and beneficial as compared tothermal swing separation in that no external heat is applied and thedesorption gas, steam, is essentially isothermal with the feed gas. Thegas-solids contactors may use moving solid sorbents, or solid sorbentscontained in packed beds or in parallel-channel beds (monoliths). Thepacked bed or monoliths can be rotating or stationary. To permitcontinuous flow of inlet and outlet streams, multiple beds can becombined with appropriate valving to switch individual beds betweenadsorption and desorption. Such multiple bed arrangements can beoperated to achieve counter-current staging. The water and energy fromthe regeneration steam can be recaptured after use and recycled backinto the process.

Although a classic displacement desorption process can be performed inan adiabatic manner, in some aspects displacement desorption can becombined with temperature swing adsorption. In such aspects, both atemperature swing and steam can be used during desorption to remove CO₂from the adsorbent.

Some DD regeneration processes use contact with steam to remove theadsorbed gas from the sorbent. The regeneration mechanism can be by acombination of concentration swing and desorptive displacement of theadsorbed gas with steam. The disclosure can further relate to a methodto recycle the steam and recover its energy through a multi-stagecondenser/heat exchangers system. The advantage of this option is thatit increases system efficiency.

DD processes can be used for removal of CO₂ from a combustion flue gasor natural gas stream or other streams. An advantage is that theadsorbent can be rapidly regenerated essentially isothermally with steamand discharge a moist CO₂ stream wherein the CO₂ concentration is higherthan that in the original feed gas. Another advantage of the sorbent isthat it can be used in an adiabatic reactor design. The sorbent adsorbswater during regeneration with steam and then desorbs water during CO₂adsorption so that the net reactions are exothermic during steaming andendothermic during adsorption. In this way the system does not requireexternal thermal management on the adsorber and regenerator beds. Thismodest temperature swing is also important because it thermally assistsboth adsorption and desorption, again without the addition of externalthermal management.

High process efficiency can be important in order for CO₂ capture to beeconomical. The regeneration system can be designed to recycle the steamand recover its energy.

The process can be carried out in a cyclic adsorption/regeneration cycleand can include various intermediate purges and stream recycles. Such aprocess can be performed with co-directional flow of the feed gas andregeneration steam, but can be preferably performed with counter-currentfeed adsorption/steam regeneration steam flows.

The process can include the steps of passing a gas stream comprising CO₂over a sorbent to adsorb the CO₂ to the sorbent, and then recovering theCO₂ by desorbing the CO₂ from the sorbent. As noted above, and discussedin more detail below, the adsorption/desorption process can be based onconcentration swing and desorptive displacement. Concentration swingadsorption (CSA) processes including the adsorption and desorption stepsare governed by change in fugacity of the adsorbate, in this case, CO₂,in the gas stream, in comparison to the adsorbent. The adsorbate, inthis case CO₂, is adsorbed when its fugacity is high in the gas streamand low in the adsorbent. Conversely, it is desorbed when its fugacityis reduced in the gas stream relative to the amount in the adsorbent. Byway of example, an adsorbent having a high level of CO₂ might stilladsorb additional CO₂ when the gas stream has a relatively higherfugacity of CO₂ versus the adsorbent. And an adsorbent having a lowlevel of CO₂ can adsorb CO₂ when the gas stream has a low fugacity ofCO₂ so long as the relative fugacity of CO₂ in the sorbent is stilllower than the CO₂ in the gas stream. One of ordinary skill in the artwould also recognize that “relative fugacity” does not imply relativeconcentration in the absolute value sense, i.e. does not mean that a 2%adsorbed CO₂ content is necessarily larger than a 1% CO₂ gas level,because the ability of the gas to retain CO₂ versus the ability ofadsorbent to adsorb additional CO₂ will be governed by variousequilibrium relationships.

DD processes also include desorbing the CO₂ from the sorbent. This stepmight also be referred to as a regeneration step because the sorbent isregenerated for the next passage of a CO₂ gas stream across the sorbent.The desorption of CO₂ from the sorbent comprises treating the sorbentwith steam. This desorption step can be driven by a one or more forces.One desorption force is concentration swing, as with the adsorption stepabove. The partial pressure of CO₂ in the incoming steam is nearly zero,and thus the adsorbed CO₂ can shift to the steam phase. The seconddesorption force is desorption by displacement. The water molecules inthe steam can adsorb onto the sorbent and displace the CO₂ from thesorbent.

As an optional step, the processes, methods and systems of thedisclosure can also include one or more purging step, in which anon-adsorbent gas, i.e. not steam or a CO₂ feed stream, can be passedacross the sorbent. The gas can be any gas known to one or ordinaryskill in the art, such as for example an inert gas or air. In anembodiment, the purge gas can be a nitrogen stream, an air stream, or adry air stream. Alternatively the purge gas can be a CO₂ feed gas orsteam that is recycled into a process step. The purge step can beconducted at any time. For example, prior to the passing of the CO₂ feedstream across the sorbent, a purge gas can be passed to remove residualand adsorbed water vapor. This purge gas can be run back into theregeneration side in order for the water vapor to be readsorbed onto theregeneration side. The purging step can also occur between theadsorption step or steps, and the desorption or regeneration step orsteps. The purge gas can be non-reactive, but can still optionallyremove adsorbed CO₂ from a sorbent based on concentration swing. Thus,in an embodiment, the purging step can be conducted after adsorptionsteps, and can be conducted to remove residual gas prior to desorption,which can be optionally recycled into the process. Moreover, the purgestep can also be optionally diverted into two streams: 1) an initialpurge stream to remove the first gas, and 2) a separate purge streamthat can contain the initial purified or desorbed CO₂, which could beoptionally captured as part of the final product stream. Furthermore, inan embodiment, a purging step can be conducted after the desorption orregeneration step(s) is complete, thereby to optionally removingresidual water and/or steam which can be recycled back into the process.Each purging step can thereby reduce an excess gas stream which can, forexample lead to a more efficient process or produce a more CO₂ enrichedproduct stream because a final product stream is not diluted by apreceding gas source. By way of specific example, a purging stepconducted after the initial adsorption can remove residual, dilute CO₂feed stream, leading to a more concentrated CO₂ product stream. Theresulting gas stream from the purging step can be recycled into thesystem, or split into a recycle and a product stream.

Example: CO₂ Separation from Dilute Feed for Use in Biomass Growth

FIG. 9 shows an example of integration of a biomass growth system with asystem for forming an enriched CO₂-containing stream from a dilute feed.In FIG. 9, a feed 901 from an external source is introduced into one ormore adsorbent bed contactors 920. The external source can correspond toany convenient type of dilute CO₂-containing stream. Examples ofexternal sources can include air or flue gas from a combustion sourcethat results in a dilute CO₂ feed. The adsorbent bed contactors can beused to form a CO₂-depleted stream 925 and an enriched CO₂ stream 929.The enriched CO₂ stream 929 can then be passed into an algae bio-reactor940 or another biomass growth process. The resulting CO₂-lean stream 943from the algae bio-reactor 940 can optionally be used as the purgestream that is passed into adsorbent bed contactors 920 to form theenriched CO₂ stream 929.

Additional Embodiments

Embodiment 1. A method for performing a separation on a diluteCO₂-containing feed, comprising: passing a feed comprising a CO₂ contentof 5000 vppm or less and a first H₂O content into a radial flowadsorbent bed module comprising alternating adsorbent bed sections andheat transfer sections to form adsorbed CO₂ and a CO₂-depleted stream,the adsorbent beds comprising a bed inner surface that faces a centralaxis of the radial flow adsorbent bed module and a bed outer surface ata larger radial distance from the central axis than the bed innersurface, the heat transfer sections comprising a transfer section innersurface that faces a central axis of the radial flow adsorbent bedmodule and a transfer section outer surface at a larger radial distancefrom the central axis than the interior surface, the bed inner surfacesand the transfer section inner surfaces defining a central volume, theadsorbent beds comprising one or more adsorbents having amine functionalgroups, the feed being passed through the adsorbent beds underadsorption conditions at a first temperature and substantially along aradial direction of the radial flow adsorbent bed module; desorbing atleast a portion of the adsorbed CO₂ in the presence of a purge gas underdesorption conditions to form a CO₂-enriched purge gas comprising a CO₂content greater than the CO₂ content of the feed, the desorptionconditions comprising at least one of a desorption temperature higherthan the first temperature and an H₂O content in the purge gas that isgreater than the first H₂O content, the purge gas being passed throughthe adsorbent beds substantially along the radial direction of theradial flow adsorbent bed module; and passing, during the adsorbing andthe desorbing, one or more heat transfer fluids through the heattransfer sections substantially along an axial direction of the radialflow adsorbent bed module, the one or more heat transfer fluidsoptionally comprising steam.

Embodiment 2. The method of Embodiment 1, wherein the feed is passedinto the radial flow adsorbent bed through the outer surfaces of theadsorbent bed sections, or wherein the purge gas is passed into theradial flow adsorbent bed through the outer surfaces of the adsorbentbed sections, or a combination thereof.

Embodiment 3. The method of any of the above embodiments, wherein thefeed is passed into the central volume of the radial flow adsorbent bed,or wherein the purge gas is passed into the central volume of the radialflow adsorbent bed, or a combination thereof.

Embodiment 4. The method of any of the above embodiments, whereinpassing the feed into a radial flow adsorbent bed module comprisespassing the feed into a plurality of radial flow adsorbent bed modulesarranged in a Napoleon configuration; or wherein passing the feed into aradial flow adsorbent bed module comprises passing the feed into aplurality of radial flow adsorbent bed modules arranged in an annularNapoleon configuration comprising a common central annular volume.

Embodiment 5. The method of any of the above embodiments, wherein thedesorption conditions comprise displacement desorption conditions, theH₂O content in the purge gas being greater than the first H₂O content,and wherein a difference between an average adsorbent bed temperature atthe end of the adsorption step and an average adsorbent bed temperatureat the end of the desorption step is 5° C. or less.

Embodiment 6. The method of any of the above embodiments, wherein thedesorption conditions comprise displacement desorption conditions, theH₂O content in the purge gas being greater than the first H₂O content,and wherein a) a difference between an average adsorbent bed temperatureat the beginning of the adsorption step and an average adsorbent bedtemperature at the end of the adsorption step is 5° C. or less, b) adifference between an average adsorbent bed temperature at the beginningof the adsorption step and an average adsorbent bed temperature at theend of the adsorption step is 5° C. or less, or c) a combination of a)and b).

Embodiment 7. The method of any of Embodiments 1-5, wherein theadsorption conditions comprise temperature swing adsorption conditions,and wherein i) a difference between an average adsorbent bed temperatureat a beginning of the adsorption step and an average adsorbent bedtemperature at the end of the adsorption step is 10° C. or less, ii) adifference between an average adsorbent bed temperature at a beginningof the desorption step and an average adsorbent bed temperature at theend of the desorption step is 10° C. or less, or iii) a combination ofi) and ii).

Embodiment 8. The method of any of the above embodiments, A) wherein theone or more adsorbents comprising amine functional groups comprise metalorganic framework adsorbents; B) wherein the one or more adsorbentscomprising amine functional groups comprise amine functionalizedadsorbents, double amine functionalized adsorbents, or a combinationthereof; or C) a combination of A) and B).

Embodiment 9. The method of any of the above embodiments, furthercomprising introducing the CO₂-enriched purge gas into a bio-reactor forbiomass growth.

Embodiment 10. The method of any of the above embodiments, wherein thepassing the feed through the adsorbent beds under adsorption conditionsand passing the purge gas through the adsorbent beds under desorptionconditions comprise simulated moving bed conditions.

Embodiment 11. The method of any of the above embodiments, wherein theCO₂-depleted gas comprises a temperature greater than the firsttemperature, and wherein at least a portion of the CO₂-depleted gas isused as the purge gas.

Embodiment 12. A system for separating CO₂ from a dilute feed,comprising: a plurality of radial flow adsorbent bed modules arranged ina Napoleon configuration, a radial flow adsorbent bed module comprising:a plurality of adsorbent bed sections, the adsorbent bed sectionscomprising a bed inner surface that faces a central axis of the radialflow adsorbent bed module and a bed outer surface at a larger radialdistance from the central axis than the bed inner surface, the adsorbentbeds comprising one or more adsorbents having amine functional groups,and a plurality of heat transfer sections, the plurality of heattransfer sections alternating with the plurality of adsorbent bedsections in the radial flow adsorbent bed module, the heat transfersections comprising one or more heat transfer fluid conduits orientedsubstantially along an axial direction of the radial flow adsorbent bedmodule, the heat transfer sections comprising a transfer section innersurface that faces a central axis of the radial flow adsorbent bedmodule and a transfer section outer surface at a larger radial distancefrom the central axis than the interior surface, wherein the bed innersurfaces and the transfer section inner surfaces define a centralvolume, and wherein the radial flow adsorbent bed module comprises asubstantially annular shape.

Embodiment 13. The system of Embodiment 12, wherein the plurality ofradial flow adsorbent bed modules are arranged in an annular Napoleonconfiguration comprising a common central annular volume.

Embodiment 14. The system of Embodiment 12 or 13, A) wherein the one ormore adsorbents comprising amine functional groups comprise metalorganic framework adsorbents; B) wherein the one or more adsorbentscomprising amine functional groups comprise amine functionalizedadsorbents, double amine functionalized adsorbents, or a combinationthereof or C) a combination of A) and B).

Embodiment 15. The method of any of Embodiments 1-11 or the system ofany of Embodiments 12-14, wherein the inner surfaces of the adsorbentbeds comprise arcuate surfaces, or wherein the outer surfaces of theadsorbent beds comprise arcuate surfaces, or a combination thereof.

Although the present invention has been described in terms of specificembodiments, it is not so limited. Suitable alterations/modificationsfor operation under specific conditions should be apparent to thoseskilled in the art. It is therefore intended that the following claimsbe interpreted as covering all such alterations/modifications as fallwithin the true spirit/scope of the invention.

1. A method for performing a separation on a dilute CO₂-containing feed, comprising: passing a feed comprising a CO₂ content of 5000 vppm or less and a first H₂O content into a radial flow adsorbent bed module comprising alternating adsorbent bed sections and heat transfer sections to form adsorbed CO₂ and a CO₂-depleted stream, the adsorbent beds comprising a bed inner surface that faces a central axis of the radial flow adsorbent bed module and a bed outer surface at a larger radial distance from the central axis than the bed inner surface, the heat transfer sections comprising a transfer section inner surface that faces a central axis of the radial flow adsorbent bed module and a transfer section outer surface at a larger radial distance from the central axis than the interior surface, the bed inner surfaces and the transfer section inner surfaces defining a central volume, the adsorbent beds comprising one or more adsorbents having amine functional groups, the feed being passed through the adsorbent beds under adsorption conditions at a first temperature and substantially along a radial direction of the radial flow adsorbent bed module; desorbing at least a portion of the adsorbed CO₂ in the presence of a purge gas under desorption conditions to form a CO₂-enriched purge gas comprising a CO₂ content greater than the CO₂ content of the feed, the desorption conditions comprising at least one of a desorption temperature higher than the first temperature and an H₂O content in the purge gas that is greater than the first H₂O content, the purge gas being passed through the adsorbent beds substantially along the radial direction of the radial flow adsorbent bed module; and passing, during the adsorbing and the desorbing, one or more heat transfer fluids through the heat transfer sections substantially along an axial direction of the radial flow adsorbent bed module.
 2. The method of claim 1, wherein the feed is passed into the radial flow adsorbent bed through the outer surfaces of the adsorbent bed sections, or wherein the purge gas is passed into the radial flow adsorbent bed through the outer surfaces of the adsorbent bed sections, or a combination thereof.
 3. The method of claim 1, wherein the feed is passed into the central volume of the radial flow adsorbent bed, or wherein the purge gas is passed into the central volume of the radial flow adsorbent bed, or a combination thereof.
 4. The method of claim 1, wherein the one or more heat transfer fluids comprise steam.
 5. The method of claim 1, wherein passing the feed into a radial flow adsorbent bed module comprises passing the feed into a plurality of radial flow adsorbent bed modules.
 6. The method of claim 5, wherein the plurality of radial flow adsorbent bed modules are arranged in a Napoleon configuration.
 7. The method of claim 5, wherein the plurality of radial flow adsorbent bed modules are arranged in an annular Napoleon configuration comprising a common central annular volume.
 8. The method of claim 1, wherein the desorption conditions comprise displacement desorption conditions, the H₂O content in the purge gas being greater than the first H₂O content, and wherein a difference between an average adsorbent bed temperature at the end of the adsorption step and an average adsorbent bed temperature at the end of the desorption step is 5° C. or less.
 9. The method of claim 1, wherein the desorption conditions comprise displacement desorption conditions, the H₂O content in the purge gas being greater than the first H₂O content, and wherein a) a difference between an average adsorbent bed temperature at the beginning of the adsorption step and an average adsorbent bed temperature at the end of the adsorption step is 5° C. or less, b) a difference between an average adsorbent bed temperature at the beginning of the adsorption step and an average adsorbent bed temperature at the end of the adsorption step is 5° C. or less, or c) a combination of a) and b).
 10. The method of claim 1, wherein the adsorption conditions comprise temperature swing adsorption conditions, and wherein i) a difference between an average adsorbent bed temperature at a beginning of the adsorption step and an average adsorbent bed temperature at the end of the adsorption step is 10° C. or less, ii) a difference between an average adsorbent bed temperature at a beginning of the desorption step and an average adsorbent bed temperature at the end of the desorption step is 10° C. or less, or iii) a combination of i) and ii).
 11. The method of claim 1, wherein the one or more adsorbents comprising amine functional groups comprise metal organic framework adsorbents.
 12. The method of claim 1, wherein the one or more adsorbents comprising amine functional groups comprise amine functionalized adsorbents, double amine functionalized adsorbents, or a combination thereof.
 13. The method of claim 1, wherein the inner surfaces of the adsorbent beds comprise arcuate surfaces, or wherein the outer surfaces of the adsorbent beds comprise arcuate surfaces, or a combination thereof.
 14. The method of claim 1, further comprising introducing the CO₂-enriched purge gas into a bio-reactor for biomass growth.
 15. The method of claim 1, wherein the passing the feed through the adsorbent beds under adsorption conditions and passing the purge gas through the adsorbent beds under desorption conditions comprise simulated moving bed conditions.
 16. The method of claim 1, wherein the CO₂-depleted gas comprises a temperature greater than the first temperature, and wherein at least a portion of the CO₂-depleted gas is used as the purge gas.
 17. A system for separating CO₂ from a dilute feed, comprising: a plurality of radial flow adsorbent bed modules arranged in a Napoleon configuration, a radial flow adsorbent bed module comprising: a plurality of adsorbent bed sections, the adsorbent bed sections comprising a bed inner surface that faces a central axis of the radial flow adsorbent bed module and a bed outer surface at a larger radial distance from the central axis than the bed inner surface, the adsorbent beds comprising one or more adsorbents having amine functional groups, and a plurality of heat transfer sections, the plurality of heat transfer sections alternating with the plurality of adsorbent bed sections in the radial flow adsorbent bed module, the heat transfer sections comprising one or more heat transfer fluid conduits oriented substantially along an axial direction of the radial flow adsorbent bed module, the heat transfer sections comprising a transfer section inner surface that faces a central axis of the radial flow adsorbent bed module and a transfer section outer surface at a larger radial distance from the central axis than the interior surface, wherein the bed inner surfaces and the transfer section inner surfaces define an central volume, and wherein the radial flow adsorbent bed module comprises a substantially annular shape.
 18. The system of claim 17, wherein the plurality of radial flow adsorbent bed modules are arranged in an annular Napoleon configuration comprising a common central annular volume.
 19. The system of claim 17, wherein the one or more adsorbents comprising amine functional groups comprise metal organic framework adsorbents.
 20. The system of claim 17, wherein the one or more adsorbents comprising amine functional groups comprise amine functionalized adsorbents, double amine functionalized adsorbents, or a combination thereof.
 21. The system of claim 17, wherein the inner surfaces of the adsorbent beds comprise arcuate surfaces, or wherein the outer surfaces of the adsorbent beds comprise arcuate surfaces, or a combination thereof. 